Glass-ceramic material and articles are of increasing commercial relevance. Currently there is worldwide interest in cordierite-containing glass-ceramics, which are based on an MgO—SiO2—Al2O3 crystalline system, due to their excellent mechanical properties, low dielectric constant and low coefficient of thermal expansion (CTE). Because of these characteristics, cordierite-based glass-ceramics are widely used as kiln furniture in white ware industry, as well as in the micro-electronic packaging industry.
There are a number of different methods for preparation the cordierite glass/ceramic material. Hamzawy et al; “Densification and properties of glass/cordierite composites”; Ceramics International, Vol. 31, Issue 3, 2005, pp 383-389 discloses a solid reaction method for preparing glass/cordierite composites from separate glass and cordierite batches synthesized from pure chemicals. Hamzawy et al; “Sol-gel preparation of boron-containing cordierite Mg2(Al4-xBx)Si5O18 and its crystallization”; Material Characterization, Vol. 57, Issues 4-5, December, 2006; pp 414-418 discloses preparation of boron-containing cordierite powders from amorphous gels. Omar et al in a presentation entitled “Crystallization of cordierite-spodumene glass” at the 2nd Conference on Physics of Condensed Matter (PCM89) in Jordan on Mar. 20-24, 1989 disclosed a glass crystallization method for cordierite preparation. Using Saudi raw materials such as MgO (91%) from sea water and pure Al2O3 (99%), Naga et al.; “Production of cordierite bodies from Saudi raw materials”; Industrial Ceramics, Volume 21, Issue 1, 2001; pp. 1-4 discloses preparation of cordierite ceramics containing mainly cordierite with secondary mullite, quartz and cristobalite. Preparation of glass ceramics by means of the sintering of cordierite constituents from its chemical powder and glass powders is also known.
Preparation of a variety of cordierite-based ceramics and glass-ceramics has also been disclosed in the patent literature. U.S. Pat. No. 5,030,398 discloses the preparation of honeycomb cordierite bodies from very fine particles of kaolin and talc to restrict a total pore volume of a given pore diameter to a given range. The structures produced have very low porosity, low thermal expansion (10×10−7° C.−1) and good resistance to thermal shock.
U.S. Pat. No. 5,409,870 discloses preparation of cordierite materials from a mixture of primary raw materials including specific types of talc and clay. This cordierite material has a coefficient of thermal expansion of less than 5×10−7° C.−1. Similarly, U.S. Pat. No. 4,973,566 discloses preparation of porous cordierite ceramic containing 95% of cordierite mineral from alumina, clay, talc and a pore-forming material. The produced ceramic materials have crush load strength of >6 pounds, electrical conductivity up to 5 watt/m2/° C. and can be used as a heat source retainer. U.S. Pat. No. 5,114,643 discloses fabrication of cordierite bodies from silica, and magnesium aluminate spinel, but no clay or talc. The bodies produced contain up to 90% of cordierite mineral and have a coefficient of thermal expansion less than 16×10−1° C.−1 within the range of 25-1000° C.
Using fast firing with a heating rate of 70° C./min, U.S. Pat. No. 6,004,501 discloses preparation of cordierite ceramic from specified amounts of various cordierite-forming materials, such a talc, magnesium aluminate spinel, kaolin and mullite, at a temperature within the range of 1360-1435° C. The cordierite ceramic so produced is characterized by a low coefficient of thermal expansion (CTE) of 9×10−1° C.−1 (25-800° C.). U.S. Pat. No. 5,332,703 discloses batch preparation of low porosity, high strength and low CTE cordierite ceramic by firing a combination of the minerals clay and talc along with chemical components such as oxides, and hydroxides of magnesium, aluminum and silicon. U.S. Pat. No. 6,319,870 discloses preparation of low CTE, high strength cordierite structures from specific mixtures of SiO2, Al2O3 and MgO-yielding materials. The produced structures have 20% porosity, with a primary crystalline cordierite phase of 65-95% and a secondary phase of mullite, spinel, and sapharine.
More recently, U.S. Patent Application Publication No. 2009/0069163 has disclosed preparation of self nucleating cordierite-based glass-ceramics with possible addition TiO2 (8-9%) to increase the nucleation process. The formed phases in such glass-ceramic include cordierite, enstatite and anorthite. These glass ceramics have a circular microstructure, good microhardness, low density, good refractoriness, and good strength (similar to SiN) phases.
It can be seen from the foregoing, that cordierite-based ceramic and glass-ceramic materials have been prepared from a wide variety of starting materials, using a wide variety of techniques and procedures. Given the desirable thermal, hardness and dielectric properties which such cordierite materials can provide, it would be advantageous to continue to identify materials and processes which can be used to prepare cordierite glass-ceramics. Desirably, the starting materials used for cordierite preparation would be naturally occurring raw materials in need of little of no purification or preparation processing prior to being employed in glass-ceramic synthesis. Ideally, such naturally occurring raw materials could also all be found and recovered from the same geographic area to minimize mining, processing and transportation costs.